Technologies such as stealth buoys and underwater gliders need to modify their own buoyancy in order to operate. Strategies such as pumping fluid are typically used to change the device's net volume. This in turn requires a mechanically sophisticated (and consequently expensive) apparatus. This document introduces the concept of a buoyancy engine that exploits the enormous volume and pressure changes accompanying the reversible electrochemical interconversion of water to hydrogen and oxygen gases. Named the Water Electrolytic Transformation (WET) buoyancy engine, this device promises to deliver a new, efficient, and very inexpensive means to control buoyancy in remote sensing and surveillance devices.
Stealth buoys are surveillance devices that record data while they lie on the ocean floor where they are virtually undetectable and are less prone to drifting problems. When it becomes necessary to notify its deployer, the buoy inflates an elastic collar and rises to the surface in order to transmit its data to some receiving station. It then retracts the collar and descends to the bottom where it gathers new data. These buoys have obvious military applications such as tracking hostile ships and submarines, but also civilian applications such as detection of smuggling and monitoring marine life.
Underwater gliders are autonomous submarine vehicles that direct vertical force (buoyancy) to horizontal translation using wings. These devices have been showing promise in recent years as a means of collecting oceanographic data inexpensively (Rudnick et al., 2004, Marine Technology Society Journal 38: 73-84). There also exists the military potential for using fleets of gliders for autonomous remote sensing and surveillance over a large patrol area.
U.S. Pat. No. 5,596,943, entitled ‘Apparatus and method for floating a towed device from a submerged vehicle’ teaches a method of surfacing a vehicle towed by a submerged vehicle by displacing water from within the towed vehicle with gases evolved by electrolysis. The towed vehicle has interior balloons or bladders for capturing evolved gases which are situated such that when empty, the towed vehicle is neutrally buoyant. As the internal bladders fill with evolved gases, positive buoyancy is produced, causing the towed vehicle to surface. Thus, this patent in effect teaches a method for modifying the hydrodynamic properties of a towed body.
Published US Patent Application 2008/0088133 entitled ‘Wave activated power generation device and wave activated power generation plant’ teaches a wave activated power generation device comprising a cylindrical floating body anchored on water and extending in a vertical direction relative to a surface of the water which includes a buoyancy control chamber that allows the floating body to vertically float in the water so as to adjust its position relative to the surface of the water. The floating body includes an air chamber and an air turbine which converts air flow into electrical power. Thus, this document in effect describes a method for harvesting energy from waves and wind by adjusting the position of the apparatus to an optimal depth.
It is important to remember that air is a fluid, as is sea water, and buoyancy is simply the difference in weight between an object and the volume of surrounding media it displaces. Since water is denser than air, it provides a much greater buoyant force for a given volume.